Taiwan's defence ministry said Wednesday that it has formed a special airborne unit capable of scrambling to the contested Spratly islands in just hours, as tensions in the South China Sea mounted.

The unit has been set up under a plan named "airborne fast response and maritime support" which was unveiled for the first time in a report by the ministry to parliament, officials said.

No details of the unit, such as its size, were released to the public, but local media said that if needed, it can arrive on Taiping Island, the biggest in the disputed waters, onboard C-130 transport planes within four hours.

Despite protests from other countries with claims in the area, Taiwan in 2006 built a 1,150-metre (3,795-foot) runway on the fortified island, which is about 860 miles (1,376 kilometres) away from Taiwan.

Also on Wednesday, Taiwan's coastguards said its troops stationed on Taiping will be armed with mortars with a range of 6,100 metres (20,000 feet), nearly doubling the range of mortars currently in use.

The moves come as an increasing number of Vietnamese fishing boats have been reported by Taiwan authorities to intrude into the restricted waters of Taiping.

The number of intruding Vietnamese boats surged to 106 last year, up from 42 the previous year, according to the coastguards, which added 41 Vietnamese fishing vessels had intruded into the waters in the four months to April.

Tensions in the South China Sea have risen recently, with China and the Philippines locked in a maritime dispute over Scarborough Shoal, a reef off the Philippine coast.

The tensions began when Chinese maritime vessels blocked the Philippine navy from arresting the crews of eight fishing vessels which had entered the area.

Taiwan, Vietnam, Brunei, China, Malaysia, and the Philippines claim all or part of the potentially oil-rich Spratlys.

All claimants except Brunei have troops based on the archipelago of more than 100 islets, reefs and atolls, which have a total land mass of less than five square kilometres (two square miles).